Unsaturated monomers, particularly olefin monomers, are polymerized in a variety of polymerization processes using a wide variety of catalysts and catalyst systems. One of the most common polymerization processes used in the production of olefin based polymers such as polyethylene, polypropylene, polybutene, etc, is a solution based process. In such a process the formed polymer is dissolved in the polymerization medium. Often, the catalyst and monomer are also dissolved in the polymerization medium, but that is not a requirement of a “solution” process. In typical solution processes, the polymerization temperature may be at, above or below the melting point of the dry polymer. For example, in typical solution phase polyethylene processes, polymerization takes place in a hydrocarbon solvent at temperatures above the melting point of the polymer and the polymer is typically recovered by vaporization of the solvent and any unreacted monomer. In some cases solvents are used while in others, the monomer to be polymerized also acts as the solvent (e.g. a bulk process).
In each of these processes, there remain factors that influence not only the rate and volume at which the polymerization can run, but can also influence the properties of polymer produced. In a typical solution process, the polymer formed is dissolved in the solvent. The higher the concentration of the polymer in the solvent, the higher the viscosity of the polymerization reaction mixture (also called polymerization medium or medium) containing polymer, monomers and solvent. High viscosity in the polymerization reactor associated with solution process is often a limiting step for process efficiency and polymer production. High viscosity can lead to difficulties in efficient mixing in the reactor, difficulties in maintaining a homogeneous system, difficulties in avoiding product property drift (heterogeneity), and, process control problems. This is especially true for polymerization processes where the polymers produced are to have a molecular weight higher than the entanglement molecular weight. Higher operating temperature may help address these problems by reducing the viscosity of the polymerization medium, however the molecular weight of the polymer product tends to decrease with reaction temperature. Thus production of higher molecular weight polymers in solution processes is limited by the viscosity of the polymerization medium. This problem exists even with the advent of new catalyst systems. Metallocene catalysts (e.g. group 4-7 transition metal compounds having at least one cyclopentadienyl group attached to the metal) allow polymerizations to be performed at a high temperatures, such that a higher polymer concentration of higher molecular weight copolymers (e.g., 16-18 wt % for ethylene-propylene-diene monomer copolymers) can be achieved in the reactor effluent without significant operation difficulties as compared to a conventional solution process (e.g., 7-13 wt % at 30-50° C. for ethylene-propylene-diene monomer copolymers). Similarly, high reaction temperatures tend to improve the polymerization rate and solvent recovery in a solution process, however, the polymer concentration still tends to be much lower than that in an equivalent slurry process. Further, it is also difficult to produce high molecular weight polymers (>100 Mooney) in a solution process due to the nature of high viscosity of a polymer having a Mooney viscosity of 100 or more. Thus there is a need in the art for a means to reduce the viscosity and/or increase the polymer concentration in a solution polymerization process, among other things.
Likewise, viscosity and other characteristics of a polymer solution are also important factors in determining process parameters, such as throughput, volume, temperature and the like. In some systems, it is possible to have a higher amount of polymer solute present, however the viscosity of that solution makes it difficult to handle,—i.e. the more viscous the solution, the more difficult it is to pump and the more likely it is to foul. Thus the process may also be limited by solution viscosity and there is a need in the art for means to reduce solution viscosity while maintaining or even increasing solute concentration.
U.S. Pat. No. 3,470,143 discloses a process to produce a boiling-xylene soluble polymer in a slurry using certain fluorinated organic carbon compounds.
U.S. Pat. No. 5,990,251 discloses a gas phase process using a Ziegler-Natta catalyst system modified with a halogenated hydrocarbon, such as chloroform.
EP 0 459 320 A discloses polymerization in polar aprotic solvents, such as halogenated hydrocarbons.
U.S. Pat. No. 5,780,565 discloses dispersion polymerizations of polar monomers under super-atmospheric conditions such that the fluid is a liquid or supercritical fluid, the fluid being carbon dioxide, a hydrofluorocarbon, a perfluorocarbon or a mixture thereof.
U.S. Pat. No. 5,624,878 discloses the polymerization using “constrained geometry metal complexes” of titanium and zirconium.
U.S. Pat. No. 2,534,698, U.S. Pat. No. 2,644,809 and U.S. Pat. No. 2,548,415 disclose preparation of butyl rubber type elastomers in fluorinated solvents.
U.S. Pat. No. 6,534,613 discloses use of hydrofluorocarbons as catalyst modifiers.
U.S. Pat. No. 4,950,724 disclose the polymerization of vinyl aromatic monomers in suspension polymerization using fluorinated aliphatic organic compounds.
WO 02/34794 discloses free radical polymerizations in certain hydrofluorocarbons.
WO 02/04120 discloses a fluorous bi-phasic systems.
WO 02/059161 discloses polymerization of isobutylene using fluorinated co-initiators.
EP 1 323 746 shows loading of biscyclopentadienyl catalyst onto a silica support in perfluorooctane and thereafter the prepolymerization of ethylene at room temperature.
U.S. Pat. No. 3,056,771 discloses polymerization of ethylene using TiCl4/(Et)3Al in a mixture of heptane and perfluoromethylcyclohexane, presumably at room temperature, further a mixture of 30% perfluoromethylcyclohexane in heptane was used to cause the polymer in the slurry to float.
Additional references of interest include:
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